1. Field of the Invention
The present invention relates to a method for measuring a radiation power, a coupler for measuring a radiation power, and an apparatus for measuring a radiation power. More particularly, the present invention relates to a method for measuring a radiation power, a coupler for measuring a radiation power, and an apparatus for measuring a radiation power, wherein a technology for measuring a radiation power of, for example, a small wireless communication terminal serving as a device under test, with a simple configuration, in a short time, and with high sensitivity is adopted.
2. Description of the Related Art
With the coming of a ubiquitous network environment, a rapid increase in very small wireless communication terminals such as Radio frequency identification tags (RFIDs) and UWB (Ultra-wideband) and BAN (Body Area Network) related radio devices are expected.
Many of these devices do not have test terminals as do conventional radio devices, due to dimensional restrictions and economical reasons. Thus, there is a need to receive radio waves radiated from the devices and conduct tests on the radio waves.
Particularly, in small wireless communication terminals such as those described above, radiation power thereof is strictly defined in consideration of its influence on, e.g., other communications or human bodies. Hence, the measurement of radiation power is an important test item.
Radiated powers include equivalent isotropically radiation power (EIRP) in any direction and total radiation power (TRP) which is radiated in the entire space.
Of them, for EIRP, a measuring apparatus is complicated and measurement requires a long time and thus TRP is handled more and more.
Methods of measuring TRP used so far include the following known methods:
(1) a spherical scanning method in which a spherical surface that envelopes a device under test (DUT) is scanned with a probe to measure radiation powers at mesh points and the radiation powers at the mesh points are integrated;
(2) a method in which in a room covered with a metal a radio wave radiated from a device under test is agitated by rotation of metal blades to generate a random field and total radiation power from the device under test is estimated based on a statistical technique;
(3) a method in which total radiation power from a device under test is measured using an apparatus called a G-TEM cell that generates a TEM wave therein by a pyramid-like space covered with a metal film and a radio wave absorber; and
(4) a method using an electromagnetic coupling apparatus that has a plurality of antennas which configure array antennas, an isolator and a phase shifter which are connected to the antennas, a combiner that combines signals at the array antennas, etc., and that measures total radiation power from a device under test which is put on a center line of the array.
The spherical scanning method in (1) is disclosed in the following Non-Patent Document 1 and Non-Patent Document 2.
Also, the electromagnetic coupling apparatus in (4) is disclosed in the following Patent Document 1.
A technology for adjusting, when a device under test such as a mobile phone is contained in an electromagnetic shielding box and a performance test is performed, the position of the device under test is disclosed in the following Patent Document 2 filed by the same applicant as the assignee of the present application.    Patent Document 1    Japanese Patent No. 3436669 (Jpn. Pat. Appln. KOKAI Publication No. 11-133079)    Non-Patent Document 1    IEIC Technical Report, AP2002-61, pp. 29-34, July 2002, “Simplified High Accuracy Measuring Method for Radio Equipment Using Integral Antennas: Radiated RF Power Measurement Using a Spherical Positioner (Part 1)”, Nojima Tomoyuki, Nakajima Kyoichi    Non-Patent Document 2    IEIC Technical Report, AP2003-85, pp. 125-130, July 2003, “Simplified High Accuracy Measuring Method for Radio Equipment Using Integral Antennas: Radiated RF Power Measurement Using a Spherical Positioner (Part 2)”, Nojima Tomoyuki, Nakajima Kyoichi    Patent Document 2    Jpn. Pat. Appln. KOKAI Publication No. 2006-322921